In a free market and under current western capitalism the final consumer price (or entire consumer market supply for that matter) isn't directly linked to features.
Ie they will sell you at max price as little as they can, not at a cost based price.
(Anyway, a cars worth of solar panels is such a negligible cost in relation to cars base price or options lists that it doesn't matter that much)

And I don't ever think you need any kind of prototype or testing to show how much solar energy can a surface of a car produce and how much travel distance does that represent - to ballpark it that is just a simple online search (you have enormous quantity of solar panel efficiency data, per latitude, as well as actual electric car consumption rates).
Bcs of that obvious common sense & various types of other solar cars out there I really doubt anyone is getting deceived here on solar mileage. The company does not claim they invented any revolutionary new solar panels (I doubt they hide the wattage spec they intend to install), nor hide the car (it's a design 10+ years old, the point of which is that it has about a 0.1 drag coefficient, so about half of that of the sleekest other cars today). Their goal here is to put the existing design into production, so more of a logistical challenge - their prototypes need to prove they can build cars (to establish a production line), not to prove any overall concept of a solar car itself.
Additionally you can already get Hyundai Iconiq 5 with a solar panel sunroof for years now, it ads a mile/kilometer per day in real life (for people with a couple of miles/kilometre commutes that's actually noticeable). But for decades you could get some car models (Toyota & Audi at least) with a solar panel sunroof, mostly they just powered the 12V battery with it to run auxiliary systems (like ventilation, AC).

I think you might have jumped to the conclusion this company is trying to sell solar cars with unlimited (outside?) range.